Frequency-hopping communication systems, which transmit portions of messages or data streams across multiple frequencies in a spectrum according to a predetermined pattern, are widely used in situations where secure communications are vital. Unless one knows the precise sequence and frequencies used by the system, it is very difficult to intercept a data stream so transmitted. Furthermore, because multiple frequencies are used to transmit a single data stream, the act of jamming or spoofing a frequency-hopped message can be very difficult.
There has been some effort in increasing the efficiency of frequency-hopping networks by simultaneously transmitting multiple messages or data streams across a specific frequency spectrum. Each message is transmitted using a given sequence of frequency and timing. To minimize the probability that portions of two messages are transmitted on the same frequency at the same time, one or more of the messages may be slightly delayed, or a different frequency-hopping pattern may be used.
One challenge of such a frequency-hopping system is that of receiving and re-assembling multiple messages. Known systems employ a single receiver dedicated to receiving each message or data stream that is being received. Each dedicated receiver requires expensive synchronization to ensure it is accurately and rapidly jumping from frequency to frequency according to the predetermined frequency-hopping pattern. When multiple data streams are concurrently transmitted according to the frequency-hopping pattern, a corresponding number of dedicated receivers are required to receive each data stream. The additional cost and space requirements due to adding dedicated receivers may adversely affect product design.
For security reasons, the predetermined frequency-hopping pattern may be changed as often as 10 milliseconds. Data streams transmitted from long distances, according to one frequency-hopping pattern, may not be received until after a new frequency-hopping pattern is initiated. Increasing the range of a frequency-hopping communications system has required either (1) using additional dedicated receivers configured to sense previously-used frequency-hopping patterns, or (2) increasing the time between changes of frequency-hopping patterns.
It is therefore an object of the invention to provide a frequency-hopping communications system that can inexpensively and efficiently process multiple data streams or messages.
It is a further object of the invention to provide a frequency-hopping communications system that may be used over long distances.
It is a further object of the invention to provide such a long-range system that can be configured to rapidly change the predetermined frequency-hopping pattern.
A feature of the invention is the use of multiple non-frequency-hopping receivers, where each receiver is configured to receive portions of any message—from a plurality of messages or data streams—that are transmitted on a given frequency.
Another feature of the invention is the extraction, from a memory, of message portions belonging to a common message, by comparing the message portions with the known frequency-hopping pattern.
An advantage of the invention is the reception of multiple data streams or messages, even from long-range transmitters, using inexpensive receivers.